Radio access networks (RANs) provide for radio communication links to be arranged within the network between a plurality of user terminals. Such user terminals may be mobile and may be known as ‘mobile stations’ or ‘subscriber devices.’ At least one other terminal, e.g. used in conjunction with subscriber devices, may be a fixed terminal, e.g. a base station, eNodeB, repeater, and/or access point. Such a RAN typically includes a system infrastructure which generally includes a network of various fixed terminals, which are in direct radio communication with the subscriber devices. Each of the fixed terminals operating in the RAN may have one or more transceivers which may, for example, serve subscriber devices in a given region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The subscriber devices that are in direct communication with a particular fixed terminal are said to be served by the fixed terminal In one example, all radio communications to and from each subscriber device within the RAN are made via respective serving fixed terminals. Sites of neighboring fixed terminals may be offset from one another and may be non-overlapping or partially or fully overlapping with one another.
RANs may operate according to an industry standard protocol such as, for example, an open media alliance (OMA) push to talk (PTT) over cellular (OMA-PoC) standard, a voice over IP (VoIP) standard, or a PTT over IP (PoIP) standard. Typically, protocols such as PoC, VoIP, and PoIP are implemented over broadband RANs including third generation and fourth generation networks such as third generation partnership project (3GPP) Long Term Evolution (LTE) networks.
RANs may additionally or alternatively operate according to an industry standard land mobile radio (LMR) protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), or other radio protocols, the TETRA standard defined by the European Telecommunication Standards Institute (ETSI), the Digital Private Mobile Radio (dPMR) standard also defined by the ETSI, or the Digital Mobile Radio (DMR) standard also defined by the ETSI. Because these generally systems provide lower throughput than the 3GPP and LTE systems, they are sometimes designated narrowband RANs.
Communications in accordance with any one or more of these protocols or standards, or other protocols or standards, may take place over physical channels in accordance with one or more of a TDMA (time division multiple access), FDMA (frequency divisional multiple access), OFDMA (orthogonal frequency division multiplexing access), or CDMA (code division multiple access) protocols. Subscriber devices in RANs such as those set forth above send and receive media items (encoded portions of voice, audio, video, and/or audio/video streams) in accordance with the designated protocol.
OMA-PoC, in particular, enables familiar PTT and “instant on” features of traditional half duplex subscriber devices, but uses mobile subscriber devices operating over modern cellular telecommunications networks. Using PoC, wireless subscriber devices such as mobile telephones and notebook computers can function as PTT half-duplex subscriber devices for transmitting and receiving auditory data. Other types of PTT models and multimedia call models (MMCMs) are also available.
Floor control in an OMA-PoC session is generally maintained by a PTT server that controls communications between two or more wireless subscriber devices. When a user of one of the subscriber devices keys a PTT button, a request for permission to transmit in the OMA-PoC session is transmitted from the user's subscriber device to the PTT server using, for example, a real-time transport protocol (RTP) message. If no other users are currently transmitting in the PoC session, an acceptance message is transmitted back to the user's subscriber device and the user can then begin transmitting captured media (e.g., audio or voice captured via a microphone of the device and/or encoded video captured via an imaging device integrated with or wired or wirelessly coupled to the device). Using standard compression/decompression (codec) techniques, the captured media is digitized, encoded, and transmitted using discrete data packets (e.g., media items that together form a media stream over time), such as according to RTP and internet protocols (IP), to the PTT server. The PTT server then transmits the media items to other users of the PoC session (e.g., to other subscriber devices in the group of subscriber devices or talkgroup to which the user is subscribed), using for example a unicast, multicast (point to multipoint), or broadcast communication technique.
Narrowband LMR systems, on the other hand, operate in either a conventional or trunked configuration. In either configuration, a plurality of subscriber devices are partitioned into separate groups of subscriber devices. In a conventional system, each subscriber device in a group is selected to a particular frequency for communications associated with that subscriber device's group. Thus, each group is served by one channel, and multiple groups may share the same single frequency (in which case, in some embodiments, group IDs may be present in the group data to distinguish between groups using the same shared frequency).
In contrast, a trunked radio system and its subscriber devices use a pool of traffic channels for virtually an unlimited number of groups of subscriber devices (e.g., talkgroups). Thus, all groups are served by all channels. The trunked radio system works to take advantage of the probability that not all groups need a traffic channel for communication at the same time. When a member of a group requests a call on a control or rest channel on which all of the subscriber devices in the system idle awaiting new call notifications, in one embodiment, a call controller assigns a separate traffic channel for the requested group call, and all group members move from the assigned control or rest channel to the assigned traffic channel for the group call. In another embodiment, when a member of a group requests a call on a control or rest channel, the call controller may convert the control or rest channel on which the subscriber devices were idling to a traffic channel for the call, and instruct all subscriber devices that are not participating in the new call to move to a newly assigned control or rest channel selected from the pool of available channels. With a given number of channels, a much greater number of groups can be accommodated in a trunked system as compared with conventional radio systems.
Individual (e.g., one to one) or group (e.g., one to many) calls may be made between wireless and/or wireline participants in accordance with either a narrowband or a broadband protocol or standard. Group members for group calls may be statically or dynamically defined. That is, in a first example, a user or administrator working on behalf of the user may indicate to the switching and/or radio network (perhaps at a call controller, PTT server, zone controller, or mobile management entity (MME), base station controller (BSC), mobile switching center (MSC), site controller, Push-to-Talk controller, or other network device) a list of participants of a group at the time of the call or in advance of the call. The group members (e.g., subscriber devices) could be provisioned in the network by the user or an agent, and then provided some form of group identity or identifier, for example. Then, at a future time, an originating user in a group may cause some signaling to be transmitted indicating that he or she wishes to establish a communication session (e.g., group call) with each of the pre-designated participants in the defined group. In another example, subscriber devices may dynamically affiliate with a group (and also disassociate with the group) perhaps based on user input, and the switching and/or radio network may track group membership and route new group calls according to the current group membership.
One problem that has arisen for individual and group calls is that a target radio of the individual or group call may miss one or more media items in a stream of media items transmitted over a radio link due to any number of factors including the target radio temporarily going out of range, the appearance of a temporary interferer within the range of the target radio or the base station serving the target radio, a handover or cell reselection process, a geographic feature such as a building, hill, or tunnel temporarily blocking communications between the target radio and its serving base station, or user action at the target radio such as the swapping out of batteries. During periods of time in which no media items in the media stream are received, conventional radios may render audio and/or video static, mute themselves, and/or blank the screen, or take some other action which, in any event, produces a media hole in which the audio and/or video intended to be transmitted to and rendered at the target radio is simply never rendered at the target radio. Instead, the target radio simply waits until the temporary reception issue is resolved and begins receiving and rendering subsequent media items in the stream of media items once they are again received. Situations may arise, however, where the missed media items are critical communications that may lead to undesired consequences if not accurately rendered in their entirety. For example, a situation may arise where a dispatcher or incident scene commander transmits a voice instruction instructing first responders “not to enter the building and seek survivors,” perhaps due to known structural issues with the building's roof If, due to one of the situations noted above, a target radio of the communication receives everything in the media stream except the word “not,” the entire context of the media changes and undesired consequences may result.
Of course, if one of the temporary situations noted above extends over a longer period of time and in fact becomes not so temporary in nature, the established radio channel between the target radio and its serving base station link (e.g., the primary channel over which the call is being received) will simply be dropped, and an indication of the failure indicated to the target user via a display or audio indication. This disclosure, accordingly, is directed to those occurrences in which the temporary situation noted above occurs over a short enough period of time to prevent the link from being dropped, but over a long enough time to cause media holes that could lead to one or more potential undesired consequences. For example, the present disclosure is directed to solving media holes having a duration of under ten seconds, or under five seconds.
Accordingly, what is needed is an improved method and apparatus for achieving lossless calls when one or more media items in a stream of media items are not received at a target radio due to a temporary reception issue.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.